I. Field of the Invention
The present invention relates generally to fuel delivery systems and, more particularly, fuel delivery systems for a direct injection internal combustion engine.
II. Description of Related Art
In a direct injection internal combustion engine of the type used in automotive vehicles, at least one fuel injector is associated with each combustion chamber in the engine. Furthermore, the fuel injectors are mounted such that the fuel injector injects fuel directly into the combustion chamber rather than upstream from the intake valves as in the previously known multipoint fuel injectors. This direct injection of the fuel into the combustion chamber results in increased engine performance and enhanced fuel economy.
In a conventional direct injection engine, a fuel pump provides pressurized fuel to a fuel rail. Two or more fuel injectors are fluidly connected with the fuel rail. Furthermore, when the engine has cylinders mounted in banks, conventionally a separate fuel rail is provided for each bank of engine combustion chambers.
One of the main advantages of a direct injection fuel delivery system is that it offers better atomization and thereby complete combustion of the fuel since it is injected directly into the combustion chamber at a high pressure. These pressures are on a magnitude of 10-20 times the pressurization required for fuel rails in the previously known multipoint fuel delivery systems.
In order to provide the high pressure fuel to the fuel rail or fuel rails, it has been the previous practice to pressurize the fuel rails with a piston pump that is reciprocally driven by a cam which, in turn, is rotatably driven by the engine. One disadvantage of these previously known piston pumps, however, is that they produce pressure pulsations within the fuel delivery system. In addition, the opening and closing of the injector nozzle (during fuel delivery into the combustion chamber) also result in pressure pulsation. These pressure pulsations result in excessive noise from the fuel delivery system. This noise is particularly noticeable to occupants of the vehicle at low engine speeds.
A still further disadvantage of the previously known direct injection internal combustion engines is that it has oftentimes been necessary to provide two fuel injectors for each combustion chamber. One fuel injector is used during low engine speed when a relatively low amount of fuel is required. Conversely, the second injector is designed to inject larger quantities of fuel into its associated internal combustion chamber at higher engine speeds. Both injectors are controlled by the engine control unit for the vehicle. Typically, pulse width modulation (PWM) is used to activate the proper fuel injector valve between an open and a closed position.
The requirement for two separate fuel injectors disadvantageously increases the overall cost of the fuel injection system.